This invention relates to an improved method of electron beam lithography for applying an electron beam to a target and, more particularly, a method of electron beam lithography which can reduce proximity effect.
An electron beam exposure method of forming a pattern on a target such as a semiconductor wafer or a mask substrate by scanning the target surface with an electron beam, has attracted attention since it can form a very fine pattern on the target. This method, however, cannot form an accurate pattern smaller than 1 .mu.m width due to the proximity effect, i.e., the scattering of the electron beam in the target. A method for compensating for the inter proximity effect is disclosed in, for instance, G. Owen & Rissman, J. Appl. Phys. 54 (6) p-3573 (1983). In this method, an electron beam is applied to a target, thus exposing the target to a desired pattern at a predetermined dose. An electron beam of less dose, forming on the target an electron beam spot greater than the beam spot formed by the electron beam for drawing the pattern, is then applied to the non-pattern area (or background) at a reduced dose.
However, when this method is carried out, using a prior art electron beam exposure apparatus, two exposure steps are necessary, i.e., exposing the desired pattern area and effecting compensation exposure (or inverse exposure) of the non-pattern area. In this case, the exposure throughput is low. Particularly, where the target is exposed by a raster scanning method, the exposure throughput is reduced to one half. Where the target is exposed by a vector scanning method, the compensation exposure (i.e., inverse exposure) of the non-pattern area requires approximately three times the period for exposing the pattern area since the area ratio of the pattern area is approximately one-third the total exposed area of the target. Further, in any exposure method noted above, a computer must be operated for a long time in which CAD data format is converted to EB format.